1. Field of the Invention
This invention relates to a process for removing NH.sub.3 in an SO.sub.2 -containing gas (acidic gas) and more particularly, it is concerned with a process for the removal of NH.sub.3 from an SO.sub.2 -containing gas using a titanium-type catalyst.
2. Description of the Prior Art
Up to the present time, a thermal reaction method or catalyst method has hitherto been employed for the removal of NH.sub.3. In this catalyst method, a catalyst using alumina as a support has generally been used. However, such a catalyst has not been put to practical use because of meeting with rapid deactivation due to poisonous sulfur compounds in an atmosphere in which SO.sub.2 and H.sub.2 O coexist. Therefore, the thermal reaction method should exclusively be used so as to remove NH.sub.3 in an SO.sub.2 -containing gas.
As a process for treating an acidic gas containing SO.sub.2, for example, there is a sulfur recovery process using the so-called Claus reaction. When this process is applied to an SO.sub.2 -containing gas with no H.sub.2 S or with an H.sub.2 S concentration of less than twice as much as SO.sub.2, the SO.sub.2 -containing gas is firstly reduced by a reducing gas such as H.sub.2, CO, etc. or a carbonaceous material to convert a part or all of SO.sub.2 into sulfur compounds such as H.sub.2 S, COS, CS.sub.2, etc. and sulfur vapor and then fed to a Claus unit. When the above described reducing reaction is carried out at a high temperature, e.g. 500.degree. to 1000.degree. C., however, several hundreds to several thousands ppm of NH.sub.3 is formed and the prestage gas for the Claus reaction, containing NH.sub.3 in such a high concentration, reacts with the acidic components such as SO.sub.2, etc. in the Claus unit to form ammonium sulfate and ammonium hydrogen sulfate which will deposit in the unit and clog the unit since it is almost kept at a low temperature, e.g. 300.degree. C. or lower, thus resulting in a serious prblem on the continuous operation. Before the present invention is developed, the removal of NH.sub.3 from the pre-stage gas for the Claus reaction must have been carried out by the thermal reaction method.
On the termal reaction method, however, installation of a heating furnace is required and in the case of direct heating, the gas is diluted, while in the case of indirect heating, it is necessary to use an expensive heat resisting material for the installation. As described above, the thermal reaction method has the various problems, i.e. excessive consumption of energy, increase in cost and complication of the process.